diff --git a/Number_types/include/CGAL/CORE_BigFloat.h b/Number_types/include/CGAL/CORE_BigFloat.h
index fe5e6219254..f5796df5a3d 100644
--- a/Number_types/include/CGAL/CORE_BigFloat.h
+++ b/Number_types/include/CGAL/CORE_BigFloat.h
@@ -23,10 +23,8 @@
 
 #include <CGAL/number_type_basic.h>
 #include <CGAL/CORE_coercion_traits.h>
-#include <CGAL/CORE_Expr.h>
 
-#define CORE_LEVEL 4
-#include <CGAL/CORE/CORE.h>
+#include <CGAL/CORE_Expr.h> // used for To_interval-functor
 
 CGAL_BEGIN_NAMESPACE
 
diff --git a/Number_types/include/CGAL/CORE_BigInt.h b/Number_types/include/CGAL/CORE_BigInt.h
index 604ea59128e..5787d258964 100644
--- a/Number_types/include/CGAL/CORE_BigInt.h
+++ b/Number_types/include/CGAL/CORE_BigInt.h
@@ -24,10 +24,7 @@
 
 #include <CGAL/number_type_basic.h>
 #include <CGAL/CORE_coercion_traits.h>
-#include <CGAL/CORE_Expr.h> // used for To_interval-functor
-
-#define CORE_LEVEL 4
-#include <CGAL/CORE/CORE.h>
+ #include <CGAL/CORE_Expr.h> // used for To_interval-functor
 
 CGAL_BEGIN_NAMESPACE
 
diff --git a/Number_types/include/CGAL/CORE_BigRat.h b/Number_types/include/CGAL/CORE_BigRat.h
index 9977b105173..0950fa93b81 100644
--- a/Number_types/include/CGAL/CORE_BigRat.h
+++ b/Number_types/include/CGAL/CORE_BigRat.h
@@ -26,12 +26,7 @@
 #include <CGAL/CORE_coercion_traits.h>
 
 #include <CGAL/CORE_Expr.h> // used for To_interval-functor
-#include <CGAL/CORE_BigInt.h>
-
-
-#define CORE_LEVEL 4
-#include <CGAL/CORE/CORE.h>
-
+#include <CGAL/CORE_BigInt.h> // used for To_interval-functor
 
 //#if defined(CGAL_CORE_BIGRAT_NUMER_DENOM_ARE_MEMBERS)
 //  #define CGAL_CORE_NUMERATOR(X) ((X).numerator())
diff --git a/Number_types/include/CGAL/CORE_Expr.h b/Number_types/include/CGAL/CORE_Expr.h
index 0c6fb3fec06..4623678df88 100644
--- a/Number_types/include/CGAL/CORE_Expr.h
+++ b/Number_types/include/CGAL/CORE_Expr.h
@@ -29,8 +29,6 @@
 
 #include <utility>
 
-#define CORE_LEVEL 4
-#include <CGAL/CORE/CORE.h>
 
 CGAL_BEGIN_NAMESPACE
 
diff --git a/Number_types/include/CGAL/CORE_coercion_traits.h b/Number_types/include/CGAL/CORE_coercion_traits.h
index eb71c2e715c..c6d7d9eb1a7 100644
--- a/Number_types/include/CGAL/CORE_coercion_traits.h
+++ b/Number_types/include/CGAL/CORE_coercion_traits.h
@@ -19,22 +19,20 @@
 // Author(s)     : Michael Hemmer   <hemmer@mpi-inf.mpg.de>
 
 
-/*! \file NiX/CORE/Coercion_traits.h
- *  \brief Provides specializations of Coercion_traits for the CORE types.
- */
-
 #ifndef CGAL_CORE_COERCION_TRAITS_H
 #define CGAL_CORE_COERCION_TRAITS_H 1
 
 #include <CGAL/number_type_basic.h>
 
 #ifdef CGAL_USE_CORE
-#include <CGAL/CORE/BigInt.h>
-#include <CGAL/CORE/BigRat.h>
-#include <CGAL/CORE/BigFloat.h>
-#include <CGAL/CORE/Expr.h>
 
-//#include <NiX/CORE/Coercion_traits.h>
+#ifndef CORE_LEVEL
+#define CORE_LEVEL 4
+#endif
+
+#include <CGAL/CORE/CORE.h>
+
+//#include <NiX/Coercion_traits.h>
 
 CGAL_BEGIN_NAMESPACE